Exploration for oil and/or minerals in subsurface environments has traditionally been done with seismic imaging techniques that are now well known in the art. In some applications, and particularly where there exists zones of anomalous densities or salt, seismic techniques alone fail to provide an adequate image as regions surrounding or beneath these zones are not clearly modelled. One particular example of a zone of anomalous density is a base of salt, such as that found in the Sudbury Basin in Ontario, Canada. Beneath the base of salt are significant deposits of minerals or of oil and gas, and in the case of the Sudbury basin, most notably, nickel deposits as has been shown, for example, in the Gulf of Mexico. Determining the shape of the base of salt is important in subsalt exploration. In the absence of an accurate model of these anomalous density zones, the model or image of mineral deposits or petroleum reservoirs below these zones cannot be determined with a high degree of confidence. Where seismic techniques alone fail to provide an adequate image of the base of salt, gravity response data can be used to complement the seismic data, by assisting in identifying the boundary of the base of salt, or other anomalous density zone.
As is known, the geologic component of the gravity field produced by such zones of anomalous densities, that is the component of interest, is a small fraction (approximately 2%) of the total measured gravity field. Therefore, a high level of precision and accuracy in measurement is required in order to resolve the geology with a fair degree of confidence. The advent of new and ever improving airborne gravity instrumentation, coupled with large data storage capacity and high processing speed makes it possible to develop better resolved interpretations of the airborne gravity information to thereby result in a more accurate boundary model of zones of anomalous density, such as a base of salt. It has also become standard practice in the art to model this gravity or magnetic data using inversion when complimenting the seismic, or other base data. The difficulty with relying extensively on inversion data is that the density model produced is not unique and can result in poor interpretations of the geologic boundary.
Furthermore, inversion techniques are often complex and require significant hardware processing time and resources. This is particularly important when attempting to precisely define boundaries of anomalous density zones with greater and greater precision and accuracy.
There is therefore a need in the art for a method and system that allows for more accurate and precise modelling of subsurface environments, and particularly those that include one or more regions of anomalous density zones such as regions of salt and have a base of salt below which there may be significant petroleum resources or mineral deposits. There is a further need in the art for a method and system that provides for accurate and precise modelling of subsurface environments that is less demanding on processing time and hardware resources than prior art methods and systems. There is a further need in the art to solve one or more of the above-identified problems with the prior art and for an improved method and system for earth modelling, and particularly for earth modelling of regions having one or more anomalous density zones.